Places of residence employ water heaters. A large percentage of these water heaters use gas in preference to electricity as a source of heat. These gas-fired water heaters include an exhaust gas flue extending from the top of the heater tank and these gases are adapted to be conducted into the ambient. In actual practice, it has been found that the gases leaving a conventional water heater are at a quite high temperature, normally within the range of 450.degree. to 700.degree.F when the water heater main burner is operating. Normally, the energy contained within this heated gas is lost.
There is a need for an auxiliary type of water heater which can be attached to the main water heater which is to function to pre-heat the water which enters the main water heater, such pre-heating of the water being accomplished by the heated flue gases which are emitted from the water heater tank. Previously, it has been known to employ such an auxiliary type of water heater tank. However, in the past, these auxiliary type of water heater tanks have been of complex construction thereby substantially increasing manufacturing cost. Additionally, such water auxiliary water heater tanks of the prior art have not been designed to extract the maximum amount of heat energy from the flue gases.